Motor control centers, as well as other electrical equipment like switchgear, are equipped with draw-out type protective control devices such as fusible disconnect switches or circuit breakers. These control devices are inserted into individual cells or compartments within the center to establish mechanical and electrical contact with bus bars, load and line stabs, or similar electrical terminals. Where there are several control devices stacked together or otherwise arranged, the terminals usually remain energized when any one of the individual control devices is removed.
The exposed terminals pose a safety hazard. An operator could be severely burned or shocked if the terminals were accidentally touched while servicing the center or installing other components near the terminals. Therefore, when a control device is removed, it is desirable to close off access to the exposed terminals to prevent inadvertent contact with the energized terminals.
There are several prior art shutter arrangements which are mounted to the rear portion of the individual cells in a control center. When the control device is inserted into the cell, shutters slide to different areas to expose the terminals for connection with the control device. The sliding mechanism supporting the shutters is complex and bulky, requiring an intricate interaction with the control device during the insertion procedure for the shutters to open properly. The sliding shutters and accompanying support mechanism occupy a substantial amount of space in the rear portion of the cell. Thus, other components and features of the center are prevented from using this area.
There is a need for a space-saving shutter using an inexpensive, simple assembly which does not interfere with the other components or operation of the control center and the respective control devices. In view of increasing safety requirements for control centers already in operation that do not contain protective apparatus for exposed terminals, there is also a need for a field-installed protective shutter assembly that fits the control center designs of various manufacture.